From version 2.0beta onward, users of JSesh can create their own signs. A sign editor and an elaborate database system are planned in the future, but, on a more practical sign, it was decided to allow one to import signs created with various softwares.
So : a) JSesh has currently no sign editor but b) JSesh can import signs from :
true type fonts (see fontforge for a free editor) ;
SVG files : SVG is a relatively recent format for vector graphics. It's very powerfull and complete. Currently, JSesh understands SVG files if the sign is drawn in black over white. You can edit SVG files with a number of programs; one of the best free ones is Inkscape, which has the advantage of being multi-platform.
For compatibility with my previous software (tksesh), it can also read:
font files exported from tksesh (.tml files)
font files from the GNU font utils (.bzr files). Both types of files can be edited with the fontedit software, included in tksesh. But this is of little interest for the generic user.